1. Field of the Invention
The present invention relates generally to a semiconductor process, and more specifically to a semiconductor process that forms two cap layers on a gate structure.
2. Description of the Prior Art
With the increasing miniaturization of semiconductor devices, various Fin-shaped field effect transistor (FinFET) devices have been developed. The Fin-shaped field effect transistor (FinFET) has many advantages. First, manufacturing processes of Fin-shaped field effect transistor (FinFET) devices can be integrated into traditional logic device processes, and are therefore more compatible. In addition, since the three-dimensional structure of the FinFET increases the overlapping area between the gate and the substrate, the channel region is controlled more effectively. This way it reduces the drain-induced barrier lowering (DIBL) effect and short channel effects. Moreover, the channel region is longer for the same gate length, so the current between the source and the drain is increased.
Generally, a fin-shaped field effect transistor comprises a stacked structure including a fin-shaped structure, a gate structure and a cap layer on a substrate, and a spacer beside the gate structure. Forming the spacer method in the fin-shaped field effect transistor process includes using a spacer material that is entirely covered and then etched to form the spacer beside the gate structure. The electrical performances of the fin-shaped field effect transistor can be modified by controlling the relative height of the gate structure and the cap layer. For instance, when the height of the spacer is smaller than the thickness of the gate structure to expose the gate structure, problems such as poly-bump or circuit leakage would occur on the gate structure in sequential processes. When the spacer is higher than the cap layer, the sequential processing time and the processing cost increase, and performing the sequential process becomes harder. Sequential processes such as epitaxial process, salicide process or contact plugs process become harder to be performed as the spacer material on the substrate between the fin-shaped structures can not be etched entirely because the spacer material is etched to form the spacer. When the spacer material on the substrate between the fin-shaped structures is entirely removed by extending the processing time, over-etching of the spacer occurs which causes problems such as the gate structure being exposed.